Fuel cell power systems convert a fuel and an oxidant to electricity. One fuel cell power system type of keen interest employs use of a proton exchange membrane (hereinafter “PEM”) to catalytically facilitate reaction of fuels (such as hydrogen) and oxidants (such as air/oxygen) into electricity. The PEM is a solid polymer electrolyte that facilitates transfer of protons from the anode to the cathode in each individual fuel cell of the stack of fuel cells normally deployed in a fuel cell power system.
In a typical fuel cell assembly (stack) within a fuel cell power system, individual fuel cells have flow fields with inlets to fluid manifolds; these collectively provide channels for the various reactant and cooling fluids reacted in the stack to flow into each cell. Gas diffusion assemblies then provide a final fluid conduit to further disperse reactant fluids from the flow field space to the reactive anode and cathode; these diffusion sections are frequently advantageously embedded as a part of the design of collector electrodes pressing against the reactive anode and cathode.
PEM fuel cell stacks are typically designed with serpentine flow fields. Serpentine flow fields are desirable as they effectively distribute reactants over the active area of an operating fuel cell, thereby improving performance and stability. On the other hand, effective operation of a PEM requires operation of the flow field channels and gas diffusion assemblies in non-flooded states. However, in this regard, an operational problem arises as certain portions of serpentine flow fields accumulate liquid water during fuel cell operation. This liquid water is undesirable, as it alters flow distribution of the reactant gases, and it can also remain in the stack even after a considerable purge. In freezing conditions, water plugs remaining in a channel after stack shutdown are a basis for severe mechanical damage to the fuel cell as the remaining liquid water is transformed into ice. U-bend (180-degree turn) portions of the serpentine flow channels are particularly prone to such water build up.
What is needed, is a way of preventing significant water build up during operation of a fuel cell power system along with a way of removing any water build up when it does occur. The present invention is directed to fulfilling this and other related needs in a fuel cell.